Concrete planters are popular and stylish choices for patios, walkways and gardens. Make your own concrete planter with common household objects. Create a basket planter with two different-sized bowls. Make a rectangular concrete planter from two rectangular plastic containers. You can also use a sturdy cardboard box and any shape of bowl to make a square planter.
Line the inside of a sturdy cardboard box with plastic wrap. Coat the plastic wrap with a concrete release agent. Release agents are available commercially, but you can also use a thick coating of non-stick cooking spray. The release agent allows the concrete to separate from the mold.
Mix the concrete topping mix according to the manufacturer's directions. Topping mix is a good choice as it does not contain stones. Your concrete planter will be smoother if you use a mix with no stones.
Spread 2 inches of mixed concrete topping evenly along the bottom of the cardboard box. Coat the three 2-inch-long dowels with the concrete release agent. Insert the dowels into the center of the concrete mix. Arrange the dowels in a circle. Separate the dowels 3 inches. The dowels create the drainage holes for your concrete planter.
Coat the outside of a medium-size bowl with the concrete release agent. The bowl can be any shape as long as it fits inside the cardboard box with at least 1 inch of clearance around the sides.
Place the bowl on top of the concrete mix in the bottom of the cardboard box. Fill in between the sides of the bowl and the cardboard box with concrete topping mix. Allow the concrete to dry 48 hours.
Remove the bowl. Remove the concrete planter from the cardboard box. Remove the plastic and the dowels from the planter. A scrub brush will help remove any stubborn bits of plastic wrap from the concrete. Wait at least one week before using your concrete planter. The concrete still needs time to cure.